1. Field of the Invention
The present invention relates to an optical sensing system, and more particularly, to an optical sensing system using positioning holes and encoding holes to generate encoding signals.
2. Description of the Prior Art
Please refer to FIG. 1 and FIG.2. FIG.1 is a side view of a prior art optical sensing system 10. FIG. 2 is a front view of the optical panel 14 shown in FIG. 1. The optical sensing system 10 comprises a chassis 12, a wheel-shaped optical panel 14, and a sensing device 16. The optical panel 14 is rotatably mounted on the chassis 12. It comprises a plurality of encoding holes 24 circularly installed around the periphery of the optical panel 14. The sensing device 16 is installed on the chassis 12 for detecting rotations of the optical panel 14. It comprises a printed circuit board 22, a light source 18 installed on the board 22 for emitting light to the optical panel 14, and a light detector 20 installed on the board 22 which comprises three sensors 19a, 19b and 19c for detecting the light emitted from the light source 18 and transmitted through the encoding holes 24.
Please refer to FIG. 3. FIG. 3 is a timing diagram of three output signals 27, 28, 29 generated by the three sensors 19a, 19b and 19c when the encoding hole 25 of the optical panel 14 shown in FIG. 2 passing across the light detector 20. The timing diagram clearly shows that when the front and rear edges of the encoding hole 25 passing across the light source 18, the sensors 19b and 19c of the light detector 20 generate jitters at the front and rear ends of the output signals 28 and 29. It is because the front and rear edges of the encoding hole 25 will interfere with the light transmitted through the encoding hole 25 and cause instability over the light received by the sensors 19b and 19c of the light detector 20. Since the encoding hole 25 is used for identifying a specific position of the optical panel 14, the jitters existed in the output signals 28 and 29 make it difficult to judge the position of the optical panel 14.